This baby was one of the lucky chicks I happened to find wandering in the yard. Hatched by one of my "missing" hens. Her hatch mate was eaten by the flock :( I know! Very sad, but it's the life of a chicken. In fact I had to chase a chicken around who had this chick in it's mouth about to eat it. She is an Ameraucana/Barnevelder mix and is super adorable! (her daddy is to the left of her actually calling her to come see what he found to eat). She is fast, she is very fast...she has to be yet. When she is the same size she will fit right in though.
Adding young chickens to your already established flock could be big trouble and it should only be done if you have some time to watch how it goes. If you don't have the time it simply should not be done in my opinion. You will end up with a dead or at the very least very injured chick. My hens have ate bigger prey then this little girl. Adding new ones to a free range flock is MUCH different then adding to a caged flock. I have done both and let me tell you...it was horrific adding to a "non free range" flock and I did not get good results. And this is after allowing them to see the newbie through wire for weeks and weeks prior to adding. If I were the type of person who would just throw and go I would have had dead chicks/pullets on my hands. Only the strong (or fast) survive but they usually don't look pretty when it's all said and done. I can't do it and never will after seeing what I have seen.
What I recommend is to add the babies to an outdoor "free range" flock and I'm here to tell ya. It goes MUCH better! IF you have no choice but to add to an enclosed flock then I would not add anything until they were the same size (which means waiting until the newbie is at least 5 months old). I have done this MANY times now and I have consistent results from my flocks in both types of settings.
The first few weeks (about six or until chick is fully feathered for sure) I do keep the baby in a smaller cage with it's food/water while the others check it out. Then on day one (of adding to a free range flock) I open the door and allow the chick to explore on it's own (and be sure you have time to watch what's going on) I just grab my lawn chair and a book and I wait...hrs...I wait, and I watch. The first day I only allow it out for a few hours (or as much time as your willing to give that day) and each day I go a little longer. IF the chick wanders outside with the others you will most likely have to pick it up and put it back in at dusk. For some reason (maybe the big ones won't allow it in or maybe it's that their instinct to roost is not all there yet) but the babies never seem to go in the first two or three days on their own. After about two or three days they finally get the message. When I have to put the chick back in I put it back into it's cage if I don't plan on letting it out right at sun up so it doesn't get picked on. The smaller the coop the more it will prob get picked on. My coop is huge so there are plenty of hiding spots (which baby does use). It's been a few weeks now since adding baby and as you can see from the picture she has now been excepted into the flock but is (and there is no doubt about this) on the bottom of the pecking order and prob will always be unless someone gets sick. But she's thriving and doing wonderfully :D